A stepper motor stator comprises a hollow cylindrical stator core having an even number of inwardly directed coil supports on which coils are wound. Selected predetermined sets or groups of coils are connected in series by intermediate portions of coil wire which extend around the periphery of the stator and lead wires are connected to the end portions of the coil wires which extend from the coils at the ends of the sets. Stepper motors are commonly classified with reference to the number of phases and the number of coils on the stator. The number of phases of a stepper motor is equal to the number of continuous coil wires, each coil wire being wound on one set of coil supports to produce a set of coils. For example, a four phase stepper motor having eight coils would have four continuous wires in its windings with each wire wound onto two coil supports and forming two coils per phase. A four phase stepper motor having sixteen coils would have four wires in its winding with each wire wound on four of the coil supports and thereby forming four coils per phase. A three phase stepper motor having twelve coils on its stator would comprise three continuous coil wires, each of which would be wound on four coil supports and a two phase motor having eight coils on its stator would similarly have two continuous wires with each wire wound on four coil supports.
The coils of a stepper motor stator are wound on the coil supports by sophisticated winding machines which draw wire from an endless source and wind the coils on the coil support such that the sets of coils are connected to each other by intermediate portions of the coil wire. When a stator is taken from a winding machine, there are portions of the coil wire extending around the periphery of the core which must be cut away and discarded as scrap, leaving the ends of the wires extending from the windings. These coil wire ends are then connected to lead wires by a suitable connecting process, for example, by crimping connecting devices onto the lead wires and the ends of the coil windings or by soldering the lead wires and the ends of the coil windings to terminal areas on a small circuit board mounted on the stator.
It can be appreciated from the foregoing brief description of the manufacturing process for stepper motor stators that the formation of the electrical connections between the ends of the coil wires and the lead wires is a time-consuming and costly process particularly in the case of four phase stepper motors, since a motor of this type has eight coil wire ends to which electrical connections of the lead wires must be made. The manufacturing process is also time-consuming for three phase and two phase motors. The steps of cutting away and discarding as scrap selected portions of the coil wire are usually carried out manually and inevitably, mistakes are made while these steps are being carried out. Careful testing of the stator is therefore required after the lead wires are connected to the coil windings and occasional reworking must be carried out to correct errors. It has been said that more than fifty percent of the cost of producing some types of stepper motor stators is in the labor cost of making the electrical connections between the ends of the coil wires and the lead wires.
The present invention is directed to the achievement of an improved stepper motor stator and to a manufacturing process for producing stepper motor stators at reduced cost.
In the practice of the invention, housings are mounted on one face of the stator core between adjacent pairs of coil supports. The housings are of the type which have a terminal-receiving cavity and coil wire-admitting slots in the sidewalls of the housing which communicate with the cavity so that the coil wire can be laced through the cavity and upon subsequent insertion of a terminal into the cavity, electrical contact with the coil wire is established.
The precise procedure which is followed to produce a stepper motor stator in accordance with the invention will depend upon the type of motor being manufactured, the number of phases and the number of coils. Following is a brief description of the procedure followed to produce a stator for a four phase stepper motor stator.
Wire from an endless source is laced through the wire-admitting slots of a first housing and then laced to a first coil support on which a coil is wound. After this first coil has been wound, the wire is laced around the periphery of the stator to another coil support, which is herein identified as a first opposite coil support, which is diametrically opposite to the first coil support. The wire from the endless source is then wound on the first opposite coil support and then laced through a first opposite housing which is immediately adjacent thereto. The wire is then passed around the periphery of the stator core, laced through a second housing and to a second coil support. The entire process of winding a coil, lacing the wire around to an opposite coil support, winding another coil, and then lacing the wire through an adjacent housing is repeated until coils have been wound on all of the coil supports. At the conclusion of the coil winding process, the coils which are wound on opposite pairs of coil supports will be connected in series and, in addition, excess wire will extend between the housings which must be removed. Terminals are then inserted into the housings and at the same time the excess wire on the periphery of the stator core which extends directly between the housings is removed by cutting the wires where they exit from the housings. The lead wires are then connected to the terminals, and to the ends of the coil windings, by inserting the lead wires into lead wire-receiving slots in the terminals. These lead wires can then be dressed through a strain relief means mounted on a stator face.
The foregoing brief description relates specifically to the manufacture of a four phase, eight coil stepper motor stator and the same general method, with modifications as discussed below, is used for other types of stepper motors.